The Ordnance QF 20 pounder (known as 20 pounder, 20 pdr or simply 20-pr) was a British 84 mm (3.307 inch)

tank gun A tank gun is the main armament of a tank. Modern tank guns are high-velocity, large-caliber artilleries capable of firing kinetic energy penetrators, high-explosive anti-tank, and cannon-launched guided projectiles. Anti-aircraft guns can also ...

. It was introduced in 1948 and used in the

Centurion A centurion (; la, centurio , . la, centuriones, label=none; grc-gre, κεντυρίων, kentyríōn, or ) was a position in the Roman army during classical antiquity, nominally the commander of a century (), a military unit of around 80 ...

main battle tank, Charioteer medium tank, and Caernarvon Mark II heavy tank. After the 20 pounder gun was found to have inadequate performance against the

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

T-54 The T-54 and T-55 tanks are a series of Soviet main battle tanks introduced in the years following the World War II, Second World War. The first T-54 prototype was completed at Nizhny Tagil by the end of 1945.Steven Zaloga, T-54 and T-55 Mai ...

the gun was mostly replaced in service by the larger calibre 105 mm L7 gun.

Design and development

The gun was developed by the Royal Ordnance Factories. As fitted to the Charioteer, it ran through two models: * Model A without a fume extractor. * Model B with a fume extractor. The L7 105 mm tank gun was developed from the 20 pounder. In 1954, the original version of the 105 mm was made by re-boring the tube of a 20 pounder barrel.

Service history

The gun was fitted predominantly to the Centurion tank, seeing action with British and Australian forces during the Korean and Vietnam War. When a Soviet T-54A main battle tank was driven to the British embassy in

Budapest Budapest (, ; ) is the capital and most populous city of Hungary. It is the ninth-largest city in the European Union by population within city limits and the second-largest city on the Danube river; the city has an estimated population ...

by Hungarian rebels during the

Hungarian Revolution of 1956 The Hungarian Revolution of 1956 (23 October – 10 November 1956; hu, 1956-os forradalom), also known as the Hungarian Uprising, was a countrywide revolution against the government of the Hungarian People's Republic (1949–1989) and the Hunga ...

, analysis of its armour and 100 mm gun led British officials to determine that the 20 pounder was ineffective at defeating Soviet armour. This led to the development of the 105 mm L7 tank gun, which was designed to fit specifically into the turret mountings of the 20 pounder, facilitating for easily upgunning existing tanks equipped with the 20 pounder. One 20 pounder gun was fitted to a Swiss pre-production

Panzer 58 The Mittlerer Panzer 1958 or Panzer 58 was a medium tank of Swiss design. Twelve tanks were produced and later converted to Panzer 61s. History and development After World War II, Switzerland was only equipped with outdated fighting vehicles of ...

, replacing a domestic 90 mm Kanone 1948 gun, before it was equipped with the 105 mm L7.

Performance

The 20 pounder's

APCBC Armour-piercing, capped, ballistic capped (APCBC) is a type of configuration for armour-piercing ammunition introduced in the 1930s to improve the armour-piercing capabilities of both naval and anti-tank guns. The configuration consists of an ar ...

projectile had an initial

muzzle velocity Muzzle velocity is the speed of a projectile (bullet, pellet, slug, ball/shots or shell) with respect to the muzzle at the moment it leaves the end of a gun's barrel (i.e. the muzzle). Firearm muzzle velocities range from approximately to i ...

of 1,020 metres per second and could penetrate of

rolled homogeneous armour Rolled homogeneous armour (RHA) is a type of vehicle armour made of a single steel composition hot-rolled to improve its material characteristics, as opposed to layered or cemented armour. Its first common application was in tanks. After World ...

(RHA). However, these conventional rounds were rarely used. The APDS projectile had a muzzle velocity of and the APDS Mk.3 shell could penetrate of RHA at a distance of , and of penetration at , equating to a line of sight penetration of 330 mm and 290 mm respectively. Against sloped armour, the APDS had reduced effectiveness: penetrating and of RHA at and respectively, against a plate angled 60 degrees from the normal, this is only , and of line of sight penetration. At given ranges, the 20 pounder APDS Mk. III shot only had 53% of its line of sight penetration against a sloped plate, compared to at the normal. Line of sight penetration refers to a flat line drawn through a piece of sloped armour, indicating the effective thickness. The 20-pounder could also fire

high-explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...

and

canister shot Canister shot is a kind of anti-personnel artillery ammunition. Canister shot has been used since the advent of gunpowder-firing artillery in Western armies. However, canister shot saw particularly frequent use on land and at sea in the various ...

shells.

Ammunition

*Shot Mk. 1 : an Armour-Piercing Capped Ballistic Capped (APCBC) round. *APDS Mk. 1 : an

Armour-Piercing Discarding Sabot Armour-piercing discarding sabot (APDS) is a type of spin-stabilized kinetic energy projectile for anti-armour warfare. Each projectile consists of a sub-calibre round fitted with a sabot. The combination of a lighter sub-calibre projectile wit ...

round. It uses a

nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...

propellant (NH). The APDS Mk. 1 was fielded in 1947. *DS/T PRAC Mk. 2 : a training variant of the APDS Mk. 1, it is identifiable by the yellow band painted on its black lead sabot. It uses a

cordite Cordite is a family of smokeless propellants developed and produced in the United Kingdom since 1889 to replace black powder as a military propellant. Like modern gunpowder, cordite is classified as a low explosive because of its slow burni ...

propellant (WM). *APDS-T Mk. 3 : an improved Armour-Piercing Discarding Sabot round fitted with tracer. The APDS-T Mk. 3 was fielded in 1950. *DS/T PRAC Mk. 4 : a training variant of the APDS-T Mk. 3 except for mild steel sabot painted black with yellow band. The DS/T PRAC Mk. 4 was fielded in 1955. *Shell Mk. 1 : an High-Explosive (HE) shell using a No. 410 Mk. 1 instantaneous

fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fuze d ...

. The shell is painted olive drab or buff with red band and black RDX/BWX (explosive filler). *SMK BE Mk. 1 : a

smoke shell A shell, in a military context, is a projectile whose payload contains an explosive, incendiary, or other chemical filling. Originally it was called a bombshell, but "shell" has come to be unambiguous in a military context. Modern usage so ...

filled with three internal smoke canisters ejected by a Base Ejection (BE) device. *CAN : a

consisting of a black metal cylinder filled with 580 steel pellets (9.5 kg). It has an effective range of 229 m.

Footnotes

Notes

References

Bibliography

* * . * * * . *

External links

{{DEFAULTSORT:QF 20-pounder Cold War artillery of the United Kingdom Tank guns of the United Kingdom 85 mm artillery Weapons and ammunition introduced in 1948